At the order "Up tube," the listening tube was raised from its position beneath the vessel; the signal-boy beside the mast hoisted the cone, the position of which showed the other boats what the engine of this sub-chaser was doing; the steersman put the wheel over, and the vessel headed for the estimated locality of the U-boat. All this was done in a moment or two. If the submarine was not located, the captain ordered "Stop!" the executive called, "Down tube!" The tube, which extends through the bottom of the chaser, was lowered, and the listener strove again to hear any sound of the U-boat. When the success of our detection devices had been demonstrated, it was decided that sub-chasers were well adapted to this duty, and were to be used mainly for this purpose. On May 12, 1918, six arrived at Portsmouth, England, and with the destroyer _Aylwin_ began training tests with British submarines, south of the Isle of Wight. Eighteen chasers soon after reached Plymouth, and this under command of Captain Lyman A. Cotten was made the chief base, having eventually a force of 66 vessels. On August 20th, 30 of these chasers were ordered to Queenstown, where a base had been established under command of Captain A. J. Hepburn. The Plymouth sub-chasers were in an area of considerable submarine activity, and reported a number of contacts. The S. C. 84, 85 and 86, Ensigns E. F. Williams, A. B. Baker and Gr. H. Lane, respectively, were credited with attacking and damaging a U-boat on July 10th. Nine chasers, Units 6, 2, and 10, were on hunt off the English coast on September 6th, when the listeners heard a submarine. Unit 2 attacked, dropped depth-charges, but its flagship was damaged by an explosion, and Unit 6 took up the pursuit. Located again, the U-boat went down, and the chasers bombarded her with depth-charges. Her machinery was evidently badly damaged. Listeners could hear the crew at work on the motors which would at times turn a few revolutions; but at last they stopped dead. The U-boat was unable to move. The chasers dropped over the spot all the depth-bombs they had, and at 6:15 two boats were sent to Penzance to get a fresh supply. [Illustration: AMERICAN SUB-CHASERS AT CORFU, GREECE Eleven of these boats took part in the attack on Durazzo, the Austrian naval base in the Adriatic.] [Illustration: A FLOCK OF SUB-CHASERS WITH THEIR MOTHER SHIP The _U. S. S. Melville_ with sub-chasers at Queenstown.]